When should a urine protein test be ordered?

When to Order Urine Protein Testing

Urine protein testing should be ordered annually for all patients at increased risk for chronic kidney disease (CKD), including those with diabetes mellitus, hypertension, or family history of CKD, as part of their regular health examination. 1

Populations Requiring Screening

• Patients with diabetes mellitus should undergo annual screening for microalbuminuria 1, 2
• Patients with hypertension should be screened annually for proteinuria 1, 2
• Individuals with family history of CKD should receive annual screening 1, 2
• African American individuals and patients with hepatitis C virus coinfection are considered high-risk and should undergo annual screening 2
• Patients with known CKD should have GFR and albuminuria assessed at least annually, with more frequent monitoring for those at higher risk of progression 1

Preferred Testing Methods

• Initial screening should begin with automated dipstick urinalysis when available 3
• If dipstick is positive (≥1+, 30 mg/dL), confirmation with spot urine protein/creatinine ratio within 3 months is recommended 3
• For patients with diabetes, measurement of urinary albumin is preferred to total protein 1
• First morning void sample is preferred, but random specimens are acceptable for initial screening 3
• Timed urine collections should not be used for routine screening 1

Interpretation of Results

• Normal protein excretion is considered ≤30 mg albumin/g creatinine 1
• Microalbuminuria is defined as >30 to 300 mg albumin/g creatinine 1
• Macroalbuminuria is defined as >300 mg albumin/g creatinine 1
• Persistent proteinuria is defined as two or more positive results on quantitative tests over a 3-month period 1, 3
• At very high levels of proteinuria (spot urine total protein to creatinine ratio 500-1000 mg/g), measurement of total protein instead of albumin is acceptable 1

Follow-up Testing

• To identify persistent albuminuria, repeat to confirm values >30 mg albumin/g creatinine in 2 of 3 tested samples 1
• Patients with documented persistent microalbuminuria who are undergoing treatment for elevated blood pressure or lipid disorders should be retested within 6 months to determine if treatment goals and reduction in microalbuminuria have been achieved 1
• If treatment has resulted in significant reduction of microalbuminuria, annual testing is recommended 1
• If no reduction in microalbuminuria has occurred, blood pressure and lipid levels should be evaluated to determine if targets have been achieved 1

Special Considerations

• Patients should refrain from vigorous exercise for 24 hours before sample collection 1
• Transient proteinuria can occur during menstruation and should be re-evaluated after the period ends 3
• The term "microalbuminuria" should no longer be used by laboratories 1
• If significant non-albumin proteinuria is suspected, use assays for specific urine proteins (e.g., α1-microglobulin, monoclonal heavy or light chains) 1, 4
• Spot urine protein/creatinine ratio >20 mg/mmol (0.2 mg/mg) is the most commonly reported cutoff value for detecting proteinuria, while a value >350 mg/mmol (3.5 mg/mg) confirms nephrotic proteinuria 5

Common Pitfalls to Avoid

• Relying solely on dipstick testing for definitive diagnosis 3
• Failing to confirm positive dipstick results with quantitative testing 3
• Diagnosing pathological proteinuria based on a single test during conditions that can cause transient proteinuria (fever, intense exercise, dehydration, emotional stress) 3, 6
• Not refrigerating urine samples for assay the same or next day 1
• Repeated freeze-thaw of specimens should be avoided 1